This invention relates to current measuring apparatus which detects when the difference in direct current in two electrical conductors exceeds a predetermined level.
It is often desirable to determine when a change in current occurs in a pair of electrical conductors connected to a common power source such as a battery. For example, in a power distribution system, the current in one conductor might decrease from 20A (amperes) to 15A and the current in another conductor pair might have a corresponding increase. Such changes could signify a variety of possible circuit failures, such as a shorted steering diode in one of the conductors. Various sensing devices, usually voltage sensitive, have been built to determine when current changes of this type occur. Besides voltage sensitive devices, differential relays have been built and are very useful in determining current changes in a pair of conductors. Unfortunately, such relays are designed for relatively low current levels (i.e., small signal applications). Particularly for currents in the 20A to 50A region such devices are completely useless. The basic reason differential relays are not made to operate at high current levels is that the large conductor size precludes winding onto a common coil form. Certainly there are techniques available which could be used to reliably make such measurements in this high current region, however, they employ sophisticated and rather expensive apparatus.
It is an object of this invention to provide a reliable and inexpensive differential current detector.